The field is that of medical instruments, pneumatic pumping of small, precise volumes in medical instruments, and temperature compensation for medical instruments and precise fluid movements.
Pneumatic pumping systems are used to pump many fluids, including fluids with medical applications. One such application is a fluid management system used to pump dialysate fluid for an automated peritoneal dialysis system. In general terms, persons whose kidneys do not function adequately may use the peritoneal membrane instead. Diffusion and osmotic exchanges take place across the peritoneal membrane between the dialysis solution and the bloodstream. These exchanges remove the waste products normally excreted by the kidneys. The waste products typically include sodium and chloride ions, and other compounds normally excreted through the kidneys, such as urea, creatinine, and water.
In a typical treatment, dialysis fluid enters the patient, dwells for a period of time, usually several hours, and is then removed. The cycle may be repeated as often as the attending physician believes is necessary. Peritoneal Dialysis (PD) may be used in the form of continuous ambulatory peritoneal dialysis (CAPD), in which a patient performs a PD cycle about four times a day, using a cycle of infusing the peritoneal dialysis fluid, dwell for a period of time, and then draining the PD fluid. Each cycle lasts for several hours. In automated peritoneal dialysis (APD), a cycler performs the drain, fill and dwell tasks while the patient sleeps at night. There are also a number of other recognized treatment regimes, such as intermittent PD (“IPD”) or continuous cycling PD (“CCPD”), in which the cycle is performed about 6 times per day and the peritoneal cavity is completely drained during the drain portions of the cycle.
Regardless of the particular regimen used, peritoneal dialysis is a difficult procedure for patients. In order to preserve patient comfort, and thus to encourage the patient to return for treatment, it is important to accurately control the volume of dialysate that is pumped into the patient. The volume of dialysis fluid is important for several reasons. Excess volume by itself could cause patient discomfort or injury, while too little volume will result in a longer and less-effective change therapy. The difference in temperature between the pneumatic pumping system at ambient temperature and the temperature at which it was calibrated (at the factory) detracts from the accuracy of the volume of the dialysate pumped to the patient. What is needed is a better way to compensate for the difference in these temperatures.